The proposed experiments are designed to investigate the interactions of metabolically related vasoactive chemicals in local control of microvascular hemodynamics in skeletal muscle of normal rats, and to determine if the local regulatory mechanisms are compromised in the spontaneously hypertensive rat. The preparation will be the open cremaster muscle, suffused with a Krebs-Henseleit solution whose components can be controlled and altered as desired. Measurements of red cell velocity (V) will be made in arterioles, capillaries, and venules by an on-line and video, off-line dual-slit photometric method. Arteriolar blood flow (Q) will be calculated from the equation Q equals V pi D squared/6.4 for vessels between 10 and 70 micron, where D is the internal diameter of the arteriole measured from the video tapes. The PO2 of the tissue and the fluid suffusing the tissue will be measured with the Whalen recessed oxygen microelectrode. These techniques will be used to measure the interaction between changes in PO2 and extracellular pH on the micro-vessels, to study the interaction of PO2 and PCO2 in the control of skeletal muscle circulation, to differentiate the effect of CO2 from that of changes in pH, and to determine if the local regulatory mechanisms are limited by sympathetic tone or increased sensitivity to circulating hormones in the spontaneously hypertensive rat. The results of these experiments will contribute to the understanding of metabolic regulation of the blood flow, and the mechanisms behind the development of hypertension in the spotaneously hypertensive rat.